A person with a prosthetic leg has a similar problem to a person who has a dropped foot, being unable to lift the toes clear of the ground during the swing phase of walking. The dropped foot problem has been addressed by functional electrical stimulation (FES).
The first reference to FES is the work by Liberson, et al, “Functional electrotherapy in stimulation of the peroneal nerve synchronized with the swing phase of gait of hemiplegic patients”, Arch Phys. Med. rehabil 42, 202-205 (1961). At this time electrotherapy was commonplace, but functional electrotherapy was a new concept. Liberson defined it as follows: “ . . . to provide the muscles with electrical stimulation so that at the very time of the stimulation the muscle contraction has a functional purpose, either in locomotion or in prehension or in other muscle activity. Functional electrotherapy is a form of replacement therapy in cases where impulses coming from the central nervous system are lacking.”
Liberson used a portable stimulator to correct drop foot during walking. A train of pulses of 20-250 μsec duration, frequency 30-100 Hz and maximum peak current 90 mA was applied through conductive rubber electrodes. The negative (active) electrode was placed over the common peroneal nerve below the knee and the large indifferent electrode either on the thigh or on the lower leg. The stimulator was worn in the pocket and a heel switch was used to trigger the stimulus during the swing phase of the gait cycle. The switch was worn on the shoe on the affected side so that the electrical circuit was interrupted during the stance phase, when the weight was on the heel, and allowed to flow when the heel was lifted during the swing phase. Liberson was enthusiastic about the results, reporting that all the subjects experienced considerable improvement in gait. Despite improvements in the apparatus used, the basic idea of FES has remained unchanged. Sixteen papers on the topic published in the period 1960-1977 have been reviewed by J. H. Burridge et al, Reviews in Clinical Gerontology, 8, 155-161 (1998).
U.S. Pat. No. 5,643,332 (Stein) also teaches FES and explains that although variants of the technique have been tried and some success has been obtained, the most common appliance fitted to people with foot drop is an ankle-foot orthosis (AFO) which is a plastics brace that fits around the lower leg and holds the foot at close to a 90° angle with respect to the long axis of the leg, and which does not employ electrical stimulation. Stein gives a number of reasons why FES had not replaced the AFO, amongst which is unreliability of the foot switch. In order to overcome this problem, Stein proposes a tilt sensor for measuring the angular position of the lower leg, but he also provides a socket for a hand or foot switch for those patients who cannot use a tilt sensor as there is insufficient tilt of the lower leg. A muscle stimulator for knee stabilization, also based on a tilt switch, is disclosed in U.S. Pat. No. 4,796,631 (Grigoryev). Muscle stimulation for the treatment and prevention of venous thrombosis and pulmonary embolism is disclosed in U.S. Pat. No. 5,358,513 (Powell, et al).
U.S. Pat. No. 6,507,757 (Swain, et al.) discuss a stimulator for stimulating the leg in a patient with drop foot that is controlled by a foot switch. The invention provides a functional electrical stimulator for attachment to the leg that includes electrodes to apply an electrical stimulus, a foot switch for sending foot rise or foot strike, a circuit responsive to the foot switch for generating stimulation pulses.
Footwear with flashing lights controlled by pressure switches is known, see U.S. Pat. Nos. 5,546,681, 5,746,499 and 6,017,128 (L.A. Gear, Inc.), U.S. Pat. No. 5,903,103 (Gamer) and U.S. Pat. No. 6,104,140 (Wut).
Gait training for amputees having at least one prosthetic leg requires a different technology to enable foot swing.